Using a SATA Port Multiplier vs. a PCI SATA Controller?

Hi everyone,

I have just been browsing around on the SageTV forum. In a post I read about something called a “SATA Port Multiplier”.

After reading a bit about SATA Port Multipliers, I found this might be quite a usable component for a unRAID server?

http://www.sata-io.org/portmultiplier.asp

http://www.addonics.com/products/host_controller/ad5sapm.asp

Instead of buying a normal PCI SATA Controller, why not use a SATA Port Multiplier in one of your existing SATA ports and get 4 extra SATA ports?

I don’t know if this I compatible with unRAID, I just thought I would share this – to me – new knowledge.

Perhaps someone else know more about this?

Regards,

Søren

Instead of buying a normal PCI SATA Controller, why not use a SATA Port Multiplier in one of your existing SATA ports and get 4 extra SATA ports?

Whow, thrilling idea.

Just in the second I read your post I had to think about such a multiplier at the e-SATA Port at the back of my machine, a small case with power supply and unRAID serving more than 15 drives. Where can I get one ;-)

Sounds to good to be true ...

Thanks for bringing this to the audience.

Harald

Without knowing anything "real" i see these possible drawbacks.

- 4 drives sharing one sata channel, if more than one is active it will be slow disks

- If unraid sees the 4 disks as one, it will require a HUGE paritydisk.

Hmm, if I do understand the details on Wikipedia right, you multiply the port and get up to 4 more disks. Look here:

http://www.sataport.com/

or do bring it to some higher level ;-)

http://www.pc-pitstop.com/sata_enclosures/scsat10pm.asp

What a thrill.

Harald

Given that unRAID is a NAS server, I don't see the limited bandwidth of a single 300MB/sec SATA port as being an issue, except during parity re-build.  That said, I would strongly suspect that not all SATA adapter chips support these things...

SirWired

I agree, I don't think the sata port bandwidth would be much of an issue - my guess is that in most cases, network and bus bandwidth, as well as limitations on the client computer(s), will limit how much data can get to/from multiple disks off the same port multiplier.

A port multiplier really would open up a lot of hardware choices for unRaid.  With four of them on a motherboard with only 4 sata connections, you could reach a 16 disk build without using a single expansion slot, wow!  Granted, that means your motherboard and port multiplier costs are $500+ in that scenario, but it is still a very interesting idea for some applications.  An ITX mobo with 2 sata connections could hit 8 disks without using an expansion slot.  wow!

If I thought anytime soon I was going to need more sata ports, I think I would give this a try.

Of course, if you are using eight disks, you will already be using a fair-sized uATX or ATX case, so you might as well get yourself a cheap uATX mobo...

SirWired

True, if one knew up front that eight disks was the plan up front. 

But for someone going for an energy efficient, compact four disk build could do that and if the needs changed in the future, would not have to throw away case, motherboard, etc, to get to eight drives, but could instead add a port multiplier and an external 4-drive enclosure connected via eSata, all done without replacing anything, just adding on.

over the past few weeks, and before coming across unRAID again (i first discovered unRAID three years ago), i happened to have evaluated the whole PM (port-multiplier) issue ad nausea...it is my understanding that a SATA chipset - on the mobo or host-controller -  has to be PM capable in order to work...the SIL3124 chipset is, so using one of their inexpensive PCI controllers with 4 external SATA ports, one can hook up 20 external drives...

as was correctly stated already, all the drives on one port share the bandwidth of the port...but since a single SATA II port can theoretically do 3Gb/sec, even 5 drives hooked up to one PM port can still operate at a combined transfer rate of over 300MB/sec...given the limitations of current drives and the PCI/PCI-X bus, this is not really something to worry about.

btw, the SATA II and PM specs allow for a total of 15 drives per PM...i have not found a card/bracket that allows for that many hardware-connections, but anyone who is into that many disks would probably lean towards SAS attached storage, where up to 128 drives can be connected by means of SAS repeaters (expensive).

if u use the SIL 3124 cards, which have gotten great reviews for allowing for very inexpensive RAID5 setups (again, you can hook up 20 drives via PMs), i found the limitation to be that only 5 drives can be included per array...so if you were thinking about an external 20 drive array (as i was), you would have to get 4 PM boxes with 5 drives each, and end up with 4 separate drive arrays (potentially giving up 4 disks, rather than 1 in a RAID5 scenario)...of course, if you're at home in the Linux world (and i am not), you can probably circumvent this limitation by not using the SIL software and building the RAID5/6 array purely in Linux's software facilities.

still, if you add up the cost of the PM's alone (about $100/ea. for a 5-to-1), you're still looking at a lot of money, and it begs the question whether you wouldn't be better off getting something like a HighPoint controller with 4 multi-lane connectors, that can support 4 drives each for a total of 16 drives, but without some of that PM voodoo (much higher bandwidth, and frankly i trust HighPoint, or Arca, etc. more than a $70 SIL controller).

long story short, after weeks of my head smoking from reading through hundreds of threads, i came across unRAID again and found that it might offer the best cost/capability/headache ratio for a setup that focuses mostly on storing huge amounts of data, which is usually: music, video, image collections for entertainment purposes...all my critical visual-productions workflow files (captured HD video, design data, etc.) will probably have to stay on a much faster RAID5 array in my workstation(s)...and when i say fast, i mostly mean how quickly can i back up a 200GB editing session to tape.

I concur... From what I read, you need a port multiplier enabled controller to start with.

A port multiplier is a silicon-based unidirectional fan-out device, typically residing on an enclosure’s backplane. It enables one host SATA PM enabled port to be connected to multiple SATA drives, similar to USB connectivity, but with the performance benefits of an aggregated switch.

As cool as it is to have 20 external drives. I start to wonder of the efficiently.

4 units of 5 drives each, that is 4 separate power supplies.

Depending on each supplies efficienty it may be better to build 1 or 2 larger machines.

Still, for a small complex the port multiplier technology seems like a good way to go.

I just came to this forum to ask about this particular thing and was hoping someone had already tested UnRAID with a port multiplier-capable card.

I've been pricing out a new media server system for my home that would be expandable, and hard originally considered RAID 5 with a Highpoint RocketRaid 2314.  It supports online expansion, as well as RAID level migration.

However, I've been playing with UnRAID inside VMWare, just to satisfy my curiosity, and I'm really considering it.  It's nowhere as difficult to use as I had thought and I really like the redundancy it offers over traditional RAID5.

Does anyone know if UnRAID supports the Silicon Image 3132 (Sil3132) chipset?  If so, I can bypass the RocketRAID and go straight to the Venus T5 which comes with a 4-port card.

If not, I can always go ahead and get my parts and just hold off on the RocketRAID until I can trial it out first on UnRAID.

Thanks,

Jon

(Hope this wasn't a hijack...I figured the premise was there).

The Venus T5 requires port multiplier support. (I happen to be looking at that myself)

I don't think the current kernel in unRaid has support for it built in yet (correct me if I'm wrong).

However, I was reading yesterday the most recent linux kernel has some patches for port multipliers.

Therefore, it should be any day soon we'll be able to use this technology.

Well, that's good and bad news then.

My current server still has about 1TB left and should get my through until summer, so hopefully everything is ironed out by then.  I'll still be putting the server together, but it doesn't necessarily have to go into use for a while.  I'd really like to give UnRAID a chance before settling on RAID5 on a Win2K3 platform.

Even though some cards say they support port multipliers and have the right chipsets, it does not mean it will work or work 100% of the time.

In the backblaze article they mention it:

http://blog.backblaze.com/2009/09/01/petabytes-on-a-budget-how-to-build-cheap-cloud-storage/

"A note about SATA chipsets: Each of the port multiplier backplanes has a Silicon Image SiI3726 chip so that five drives can be attached to one SATA port. Each of the SYBA two-port PCIe SATA cards has a Silicon Image SiI3132, and the four-port PCI Addonics card has a Silicon Image SiI3124 chip. We use only three of the four available ports on the Addonics card because we have only nine backplanes. We don’t use the SATA ports on the motherboard because, despite Intel’s claims of port multiplier support in their ICH10 south bridge, we noticed strange results in our performance tests. Silicon Image pioneered port multiplier technology, and their chips work best together."

So are there any adaptec or other cards that would do the trick, and be supported in unraid?

We should start a compatiblity matrix/spreadsheet with which cards work, which version of unraid, which cards work with port multipliers, and what settings had to be set to make them work. Does the spin down and spin up work? Does the parity check work, and does hdparam work ?

So we need a test check list and then some people to test. With the summer being almost over, I should have more time to play with unRaid now.

I would love to drop my tx4 pci 4 port cards.

So are there any adaptec or other cards that would do the trick, and be supported in unraid?

 

We should start a compatiblity matrix/spreadsheet with which cards work, which version of unraid, which cards work with port multipliers, and what settings had to be set to make them work. Does the spin down and spin up work? Does the parity check work, and does hdparam work ?

 

So we need a test check list and then some people to test. With the summer being almost over, I should have more time to play with unRaid now.

Since originally posting in this thread forever ago, I've been on a port multiplier for over a year now and have had a pretty good experience with it.  I did have one port fail on the PMP itself, in which I was able to get the module replaced fairly quickly, but it's been uneventful for the most part.

I use a Sil3132-based 2-port PCIe adapter and the PMP module uses the Sil3726 chipset.  Parity checks/caclulations are slower, but I still prefer this setup to having a ton of cards and cables in my system.  I have a 1.5TB, 2 x 500GB and 2 x 1TB drives on my PMP WITH A 1.5TB and 3 x 1TB drives off the motherboard ICH9 SATA ports.  My parity checks/calculations start out at about 28000KB/s until the smaller drives are passed and then it jumps to around 50-52K.  Spin up/down, hdparm, etc. all work.  I've never encountered anything out of the ordinary in comparison to a direct-connect disk.

I do get some warnings when starting up unRAID due to the PMP though that results in a few instances of "hard resetting link", but it always passes without issues.  It just adds 30s or so to the boot time.

I'm very happy with it and when it is time to add another bunch of disks, I'll be tying it to another 5-disk external case from PC-Pitstop to populate the other eSATA port on that controller.  I have a second Sil3132 PCIe controller ready to go for even more disks (and two single internal disks, for the time being).

Even though some cards say they support port multipliers and have the right chipsets, it does not mean it will work or work 100% of the time.

In the backblaze article they mention it:

 

http://blog.backblaze.com/2009/09/01/petabytes-on-a-budget-how-to-build-cheap-cloud-storage/

 

"A note about SATA chipsets: Each of the port multiplier backplanes has a Silicon Image SiI3726 chip so that five drives can be attached to one SATA port. Each of the SYBA two-port PCIe SATA cards has a Silicon Image SiI3132, and the four-port PCI Addonics card has a Silicon Image SiI3124 chip. We use only three of the four available ports on the Addonics card because we have only nine backplanes. We don’t use the SATA ports on the motherboard because, despite Intel’s claims of port multiplier support in their ICH10 south bridge, we noticed strange results in our performance tests. Silicon Image pioneered port multiplier technology, and their chips work best together."

 

So are there any adaptec or other cards that would do the trick, and be supported in unraid?

 

We should start a compatiblity matrix/spreadsheet with which cards work, which version of unraid, which cards work with port multipliers, and what settings had to be set to make them work. Does the spin down and spin up work? Does the parity check work, and does hdparam work ?

 

So we need a test check list and then some people to test.

That note just about sums it up, for the current state of PMP support.  I would say, stick to Silicon Image based cards, at both ends of the PMP connection (SATA disk controllers such as SiI3132 or SiI3124 based, and SATA PMP backplanes such as those based on the SiI3726) .  The Addonics cards are based on Silicon Image chipsets.  Cards using the ahci module, such as the ICH10 and JMB and newer Marvell chipsets, are generally *supposed* to support PMP, but I haven't heard much success yet.  And from what I recall, they aren't as efficient as the Silicon Image chipsets either, something about being command based, instead of FIS based.